1. Field of the Invention
The present invention relates to telecommunication networks, and more specifically, it concerns the management of multimedia sessions set up on top of a data network. This data network may be compliant with the TCP/IP (Transmission Control Protocol/Internet Protocol) family of protocols, and it may in particular be the Internet.
2. Description of the Related Art
Hereinafter, “multimedia session” refers to the transmission of data between two or more terminals involving several media types, in particular, most often voice and/or video. These multimedia sessions are commonly called VoIP for Voice over IP (Internet Protocol).
Prior to setting up the actual multimedia session, the terminals involved must exchange information in order to, in particular, set certain parameters of the multimedia session.
These parameters relate, for example, to characteristics of the medium (voice encoding format, video format, etc.). These characteristics may be determined according to the capabilities of the terminals participating in the multimedia session.
This setup phase of the multimedia session takes place in accordance with a particular protocol.
However, these protocols are quite varied. In particular, mention may be made of the H.323 protocol defined by the ITU-T (International Telecommunication Union Telecommunication Standardization Sector) and the SIP (Session Initiation Protocol) defined by RFC 2543 (Request For Comments) of the IETF (Internet Engineering Task Force).
With the aim, in particular, of hiding these differences and enabling terminals using different protocols to coexist, as is known from the prior art, protocol gateways can be placed between the various terminals.
Typically, these protocol gateways form part of call centers or controllers.
FIG. 1 schematically illustrates an example of setting up a multimedia session between two telecommunication terminals.
Terminal TA is the initiator of the multimedia session. It therefore initiates a multimedia session setup negotiation mA with the call center CC that has a protocol gateway. This multimedia session setup negotiation contains, in particular, information on the media characteristics which terminal TA can handle (video format, voice encoding type, etc.) and is compliant with the H.323 protocol.
The call center CC then negotiates with the recipient of the multimedia session, that is terminal TB, by exchanging messages mB according to the SIP protocol, and then it sets up the multimedia session MS between the two terminals TA and TB.
If necessary, if the two terminals cannot agree upon media characteristics to communicate (for example, they do not support any common video encoding format), the call center may set up the multimedia session using a media gateway.
However, there is a problem if one of the two terminals uses the H.323 protocol and the other terminal (or the other terminals in the case of a multimedia session between more than two participants) uses a protocol other than H.323 (for example, the SIP protocol).
This is because the H.323 protocol includes a phase to determine a “master” terminal and a “slave” terminal. The protocol assumes that each terminal can take on either role. The determination depends on a classification, established beforehand, of various types of terminal: the most powerful terminal takes on the role of “master” and for equal power, an arbitrary choice is made to determine which of the two terminals will assume the role of master.
This role of master is taken into account in the event of conflicts or problems. It involves a significant degree of complexity in the terminal implementing it.
In the case in which a multimedia session is set up via a protocol gateway and in which only one terminal uses the H.323 protocol, a problem arises since the phase for determining the “master” and “slave” roles can take place only between the terminal using the H.323 protocol and the protocol gateway.
Referring again to the example of FIG. 1, this means that the determination of the “master” and “slave” roles must take place between terminal TA and the call center CC containing the protocol gateway.
In accordance with the H.323 protocol, this mechanism therefore assumes that the protocol gateway can take on the role of “master”. The gateway must therefore support all the protocol and software mechanisms inherent to this function.
Since these mechanisms are complex, this type of solution involves an increase in processing resources required to enable the protocol gateway to function (memory resources, CPU (Central Processing Unit), etc.).
Moreover, since this protocol gateway is typically included in a call center, this use of resources can be to the detriment of other functions in the call center.
Furthermore, the architecture of Internet type data networks involves, generally, minimizing the processing resources required within the network, since the lifetime of the hardware within the network is assumed to be greater than that of the terminals and any increase in resources required and any update is expensive and to be avoided.
Thus, in Internet type networks, a large part of the intelligence is transferred to the terminals.
The result of this is that the increase in complexity of the protocol gateway is a major drawback.